in task, you say there are n blue cards and m red cards and you say ith red card is si. But in input, you give n s-type cards.
We are sorry, there was an error in the English statement. In the first paragraph, it said “The string written on the i-th red card is s_i, and the string written on the i-th blue card is t_i“, but here “red” and “blue” should be swapped. We are now fixing this error.
[EDIT] Now the error is fixed. We are sorry for this trouble, and will work harder to avoid similar troubles in future.